Composite fabrics made from fibrous materials formed into both woven, knitted and non-woven material, are well-known in the art. Yarns of glass, carbon and graphite are typically formed into fabrics, and a plurality of layers of fabric are stacked and cut into dry fabric preforms. The preforms are then stitched and/or impregnated with a resin binder to form a rigid composite fabric.
Typically, a glass reinforced fibrous mat is preformed and then placed in a mold for molding into a fiber-reinforced article. Glass fiber-reinforcement mats are used in situations where a desired strength is necessary, such as in boat hulls or automobile parts. For example, layers of the continuous strand mat and layers of unidirectional or multidirectional reinforcement material are fabricated separately. These layers are individually placed in a set of preform screens, which generally consist of an upper screen and a lower screen. The upper and lower screens are moved together in order to conform the layers to the shape of the preform screens. The layers are thus shaped into what is known as a preform. The preform is then placed in a mold and injected with a suitable resinous material to make the fiber-reinforced article.
As shown in U.S. Pat. No. 4,911,973, to facilitate impregnation of the fabric with resin, holes are typically punched in the fabric as two or more layers of fabric are sewn together. The holes extend through the fabric and when the fabric is impregnated with resin, the resin material flows into the holes in the blanket. The holes in the fabric aid in distributing resin throughout the fabric.
The crimping of the yarns that occurs as the warp and weft yarns cross over and under each other reduces the tensile and, more significantly, the compressive strength of a woven fabric. In the past, fabrics have been designed utilizing yarns having varying denier (fiber diameter) to increase strength and reduce crimping of the fabric.
U.S. Pat. No. 4,615,934 teaches a fabric having warp yarns of heavy denier separated by eight warp yarns of lighter denier. The fabric is incorporated into a polymeric resin by lamination, heat bonding or coating the fabric with the resin. U.S. Pat. No. 5,147,714 (related to U.S. Pat. No. 4,615,934) utilizes this same concept of alternating heavier and lighter denier yarns however the fabric is laminated between two conductive sheets of PVC film.
U.S. Pat. No. 4,460,633 teaches a non-woven reinforcement constructed of high denier warps of non-twist yarns or soft twist yarns on both sides of lower denier wefts of non-twist yarns or soft twist yarns containing an adhesive agent, in which the warps and wefts are bonded where they intersect.
U.S. Pat. No. 4,407,885 and U.S. Pat. No. 4,410,385 (related) teach a composite non-woven fabric and a method of making the composite fabric in which the layers of the fabric are impregnated with a resin binder to form a rigid composite fabric. Thermoplastic fibrous material is incorporated within the structure of non-woven layers. A plurality of layers of fabric are stacked adjacent each other to provide a preform assembly. The layers are then compacted and heated to promote the bonding of the thermoplastic material at junctures between the fibrous non-woven material.
U.S. Pat. No. 5,085,928 teaches porous layers of unidirectional aramid fibers alternated with porous layers of spunlaced nonwoven aramid fibers all of which are embedded in a thermoplastic resin.
U.S. Pat. No. 5,809,805 teaches a warp/knit stitch reinforced multi-axial non-crimp layered fabric sheet. The fabric is comprised of a plurality of plies, which have a different angular relationship to one another, disposed upon one another and knitted or stitched to form a structural sheet. The sheet is then impregnated with a resin.
U.S. Pat. No. 5,445,693 and related U.S. Pat. No. 5,055,242 teach a formable composite material having a plurality of superimposed layers each having a plurality of unidirectional non-woven yarns or threads laid side-by-side. Some of the yarns or thread extend of different layers extend in different directions. The layers are incorporated with a resin material prior to being stitched together.
U.S. Pat. No. 5,149,583 teaches a mat in which reinforcing threads are bound or laminated to form a strong shell structure. The knitting of the mat is performed with a double circular knitting machine to form a weft-knitted mat. The fabric contains a plurality of loops in which reinforcing threads run with the support of the loops and straight between the courses in a channel formed by the loops.
As taught above, it is known to have heavy denier warp yarns separated from each other by lighter denier warp yarns in a warp-inserted weft knit fabric. Also, using sewing needles to form a plurality of channels in a reinforcement blanket to aid in distributing resin throughout the blanket is known. Both methods permit resin to be distributed throughout the fabric.
There is a need to provide a fabric, having continuous fibers, to be used in a molding process, in which the design of the fabric increases the speed of resin infusion to reduce processing time in the mold.
The foregoing and other advantages of the invention will become apparent from the following disclosure in which one or more preferred embodiments of the invention are described in detail and illustrated in the accompanying drawings. It is contemplated that variations in procedures, structural features and arrangement of parts may appear to a person skilled in the art without departing from the scope of or sacrificing any of the advantages of the invention.